1. Field of the Invention
The present invention relates to a fiber plate (also known as a fiber optic plate), a manufacturing method thereof, a radiation imaging apparatus and a radiation imaging system. More particularly, the invention relates to a fiber plate utilized in the radiation imaging apparatus, which includes converting means for converting radiation into the light and a photoelectric converting device for converting light into electric signals, the fiber plate serving to guide the light from the converting means to the photoelectric converting device.
2. Related Background Art
In a radiation imaging apparatus, especially an X-ray imaging apparatus aimed at a medical treatment, there has hitherto been a demand for an X-ray imaging apparatus that is capable of capturing an X-ray dynamic image, having excellent image definition and a thin and large area input range. Further, there is also a demand for providing the thin and large area X-ray imaging apparatus at low costs, which is useful as an industrial non-destructive inspection apparatus as well as for medical treatment. In this type of X-ray imaging apparatus, when X-rays directly enter an imaging device, this causes noises when in a reading process, and there might be a case where semiconductor crystals in the imaging device are destroyed resulting in a decline of characteristics. An X-ray shielding fiber plate is therefore utilized. The use of the fiber plate enables the X-rays to be cut off without any blur of an optical image captured.
Examples of this type of fiber plate and the X-ray imaging apparatus using the fiber plate are (1) an X-ray detection apparatus (e.g., U.S. Pat. No. 5,563,414 B) having an enlarged area and structured such that the fibers of the fiber plate are inclined to prevent the non-light-receiving portions (peripheral circuits) of a CCD sensor from interfering with each other, (2) an X-ray detection apparatus (e.g., U.S. Pat. No. 5,834,782 B) having the enlarged area and structured such that the fiber plate has thickness-wise stepped portions so as to prevent the interference between the non-light-receiving portions of the CCD sensor, (3) an optical fiber plate (U.S. Pat. No. 3,397,022 B) having a structure that a light absorbing element is interposed between the fibers, (4) a fiber plate (U.S. Pat. No. 5,394,254 B) having a structure that a layer composed of glasses having physical rigidities and refractive indexes different from those of the optical fiber, is interposed between the optical fibers adjacent to each other, and (5) an X-ray imaging apparatus (U.S. Pat. No. 5,554,850 B, JP 8-211199 A, etc.) having an optical fiber scintillation plate including an optical fiber rod bundle inclined to an image surface.
FIG. 20 is a schematic sectional view of the X-ray detection apparatus having the configuration (1) given above. FIG. 20 shows a phosphor 3 constructed of a scintillator for converting the X-rays into visible light, an individual fiber plate 2A composed of optical fibers for guiding, toward an imaging device 1A, the visible light into which the phosphor 3 has converted the X-rays, and the imaging device 1A for converting the visible light guided by the individual fiber plate 2A into electric signals.
In this X-ray imaging apparatus, the individual fiber plate 2A is inclined to the imaging device 1A, and a processing circuit or the like for processing the electric signals from each imaging device 1A is provided between the individual fiber plates 2A.
FIG. 21 is a schematic perspective view of the X-ray detection apparatus having the configuration (2) given above. Note that the same components as those in FIG. 20 are marked with the same symbols in FIG. 21. As illustrated in FIG. 21, for instance, three pieces of imaging devices 1A are set as one group, and a stepped portion is provided for every group in a way that partially changes a length of the fiber plate 2, whereby a processing circuit etc. can be provided for each imaging device 1A.
In the configuration (1) given above, however, light guide surfaces (light incidence/exit surfaces) intersecting obliquely the axis of the optical fiber are provided, and the axes of the optical fibers of the fiber plate are disposed so as to intersect each other. This configuration makes it difficult to further downsize the X-ray imaging apparatus.
On the other hand, the configuration (2) given above brings about a further increase in size of the X-ray imaging apparatus. Moreover, since an alignment of each stepped portion with the imaging device requires a strict accuracy, the number of manufacturing processes increases, and a high-accuracy alignment apparatus is needed. In view of these factors, the configuration (2) given above is ruled out of the reality.
Further, in the configuration (3) given above, a gap is formed between the fiber and the light absorbing element, and the X-ray traveling through this gap penetrates the fiber plate and cannot be completely absorbed.
In the configuration (4) given above, the glass is used between the fibers, and hence the pressure and the temperature must be set high enough to soften the glass in the manufacturing process. In fact, it is difficult to attain the large area configuration. Further, a yield inevitably decreases due to distortions and deformations.
The configuration (5) discloses a structure of the optical fiber plate wherein the fiber axis is inclined to the image surface but does not disclose specific conditions taking into consideration a thickness of a bonding layer between the fibers, wherein the X-rays are sufficiently absorbed by the fiber plate.
Thus, the conventional X-ray imaging apparatuses are not necessarily sufficient in terms of downsizing the X-ray imaging apparatuses, reducing the costs thereof, improving the workability in the manufacturing process, and so on.